Low-loss electrode structures using resistive connections for optical modulation applications

ABSTRACT

An optical device includes a grounded base and an optical modulator chip having a top surface, a back surface and side surfaces. The optical modulator chip is positioned on the grounded base with the back surface facing the grounded base. The optical modulator chip includes a first ground electrode, a signal electrode and a second ground electrode located over the top surface of the optical modulator chip. The first and second ground electrodes of the optical modulator chip are interconnected with resistive layers on a surface of the optical modulator chip.

[0001] This application is a Continuation-In-Part of application Ser.No. 09/778,712 filed Feb. 8, 2001, which hereby incorporated byreference. In addition, this application claims the benefit ofprovisional application Ser. No. 60/245,207 filed Nov. 3, 2000, which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an optical modulation system,and more particularly, to the interconnection of external electrodes toan optical modulator so as to minimize loss of signal energy and toprevent the introduction of spurious modes into the signal within theoptical modulator.

[0004] 2. Discussion of the Related Art

[0005] In a general fiber optical communication system, optical signalsare sent along an optical fiber communication line to a desiredlocation. Optical modulators with performance in the 40 GHz frequencyrange and beyond, are critical components in optical communicationsystems.

[0006] To achieve high-frequency operation in a material such as LiNbO₃,the electrical and optical velocity of the modulating and modulatedsignal must be matched. This is achieved by employing thick (>10 μm)electrodes in conjunction with a buffer layer (typically SiO₂). Thebuffer layer is deposited directly on the LiNbO₃ and the electrodestructure is delineated on the buffer layer. While the buffer layerfacilitates velocity matching, it also results in decreased modulationefficiency because the applied voltage is partially dropped across thebuffer layer. LiNbO₃ is an anisotropic material, with the followingdielectric constants:

ε_(extra-ordinary=)26,ε_(ordinary=)43

[0007] Thus, planar and uni-planar transmission lines such asmicrostrip, coplanar waveguide (CPW) and coplanar strip (CPS) tend to bevery dispersive when built directly on LiNbO₃. As the frequencyincreases, the fields become more concentrated in the regions below themetal strips, where the substrate permittivity has already resulted in arelatively larger electric displacement since the fields are forced intothe LiNbO₃ to an increasing extent as the frequency increases.Therefore, a frequency-dependent effective permittivity can be definedfor the transmission line.

[0008]FIG. 1 illustrates an optical modulator of the prior art. Themodulator has a mounting base 1 that is typically conductive or made ofa non-conductive material covered with a conductive layer. The mountingbase 1 is typically at the ground potential of the device and willherein be referred to as the grounded base 1. The optical modulator hasan optical modulator chip 2, for example a LiNbO₃ chip covered with aninsulating buffer layer, mounted on the grounded base 1. The groundedbase 1 includes input/output optical terminals 345 and input/outputelectrical terminals 71. The optical modulator chip 2 has two groundelectrodes 3/3′ and a signal electrode 4 mounted on top of the bufferlayer above a waveguide 34 of the optical modulator chip 2. Thiselectrode configuration is known as the coplanar-waveguide (CPW). Whenthe electrode structure of the optical modulator chip 2 comprises justone signal electrode, and one ground plane, it is known as thecoplanar-strips (CPS) configuration.

[0009] The optical modulator chip 2 is comprised of an active section 6and non-active sections 5. The active section 6 of the device is thesection of the optical modulator chip 2 wherein the electrical andoptical signals interact to cause optical modulation. Typically, theelectrode dimensions, such as the width of the signal electrode 4, andthe electrode gap tend to be very narrow (5-25 microns) in the activesection 6. These dimensions are prohibitively small to facilitate directconnection of the device to standard electrical connectors. Hence, theelectrodes 3/4/3′ for the active section 6 are flared 31/41/31′ in thenon-active section 5 to facilitate external connection to the signalelectrode line 4 and the ground electrodes 3/3′. The flared electrodes31/41/31′ do not take part in the process of optical modulation, but arerequired to facilitate connection of the active section of the modulatorto standard electrical interface media. External electrical connectionto the flared electrodes 31/41/31′ of the optical modulator chip 2 isfacilitated by either a transition chip 7 having leads 23/24/23′connected to the flared electrodes 31/41/31′ of the optical modulatorchip 2 via wires or a direct external connection to the flaredelectrodes 31/41/31′ of the optical modulator chip 2 via wires from theelectrical terminals 71.

[0010]FIG. 2 illustrates a side view of the optical modulator in thedirection shown as A-A in FIG. 1. FIG. 2 shows electrodes 31/41/31′ on abuffer layer 8 terminating on the top surface edge of the opticalmodulator chip 2 and the grounded base 1 underlying the opticalmodulator chip 2. Although the ground electrodes 31/31′ of FIGS. 1 and 2are shown as single lines, the ground electrodes may be ground planeswhich cover most of the top surface of the optical modulator chip 2except for the signal electrode 4 and an area just outside the signalelectrode 4. For example, there can be ground planes that cover most ofthe top surface of the optical modulator chip 2 but are no closer to thesignal electrode than the ground electrodes 3/3′ shown.

[0011] The intended electrical guided mode for an optical modulatorcontains the frequency of an input or frequencies of input on theoptical modulator for operating the optical modulator. Typically, anoptical modulator has a range of sets of frequencies that can be used aselectrical inputs to modulate an optical signal. For proper operation ofthe modulator, the intended electrical guided mode of the device must besuch that the electric fields originating from the signal electrode mustproperly terminate on the adjacent ground electrodes without strayingelsewhere in the modulator chip or package. The intended electricalguided mode of the optical modulator will hereinafter be referred to asthe dominant CPW mode of the optical modulator.

[0012] Once the electric fields of the signal electrode penetratethrough the buffer layer into the optical modulator chip, several othereffects could occur. Depending on frequency, a CPW mode may couple withother extraneous electrical modes that the structure of the opticalmodulator can support. These modes could either be highly dispersiveslab modes, or could be zero-cut-off modes. Examples of extraneous modesare: transverse-electric (TE) or transverse magnetic slab modes,slot-line mode (that could occur between the two ground planes of theCPW structure), parallel-plate modes (that could be excited between theelectrodes on the top surface and the grounded base), and microstripmode (between the top electrodes and the grounded base). When couplingto extraneous modes occurs, there is a loss of power for the dominantCPW mode. Such a power loss degrades the optical modulator's modulationperformance and the clarity of the output modulated optical signal isdegraded. The amount of power lost to spurious or other extraneous modesdepends on the field overlap between the dominant CPW mode and the otherextraneous modes supported by the device.

[0013] One approach to avoid coupling to spurious or other extraneousmodes in CPW structures is by reducing the cross-sectional dimension ofthe CPW transmission line. Referring to FIG. 1, by decreasing (S+2D),which is the width of electrode 4 plus twice the distance that one ofthe optical modulator grounds 3/3′ is located from the signal electrode4, there is less field penetration into the optical modulator chip 2 andhence less of an opportunity for overlap between the guided CPW mode andother extraneous modes that can be supported by the device. Since thereis less overlap in structures with smaller (S+2D), between the CPW modeand other extraneous modes, there is less of a power loss from the CPWmode and hence less degradation of the outputted modulated opticalsignal.

[0014] However, a CPW transmission line with a smaller cross-sectionaldimension is not very practical because the device still requiresexternal electrical connection. Typically, in the nonactive sections 5of the optical modulator chip, the electrodes 3/4/3′ for the activesection 6 become respective flared electrodes 31/41/31′ to facilitateconnection to the signal electrode line and the ground electrodes. Theconnection is facilitated by the use of a transition chip 7 having leadsconnected to the flared electrodes 31/41/31′ of the optical modulatorchip 2 or a direct external connection to the flared electrodes31/41/31′ of the optical modulator chip 2. Although FIG. 1 shows twotransition chips 7, a single transition chip for external connection tothe optical modulator chip can extend down the side of the opticalmodulator chip and contain both sets of the electrodes 31/41/31′.Alternately, the modulator electrode can also be terminated with anappropriate resistance or a resistance-capacitance combination at theend of the electrode. Due to the relatively wider dimensions of theflared electrodes 31/41/31′ in the non-active sections 5 compared to theelectrodes 3/4/3′ in the active section 6, there is significant fieldpenetration into the optical modulator chip 2 (i.e. LiNbO₃) through thebuffer layer 8 in the non-active sections 5. This penetration increasesthe opportunity for extraneous mode coupling into substrate slab modesor zero-cutoff modes that the structure (i.e. the optical modulatorchip, the CPW transmission line and the grounded base) can support inboth the active section 6 and non-active section 5.

[0015] Ground plane integrity between the ground and the signalelectrode is important for satisfactory operation of the opticalmodulator. Otherwise, high-speed optical modulation in the activesections 6 of the optical modulator chip will be seriously hampered.This is because over the frequency range of interest, the electricalvelocity and hence impedance varies at the input to the modulator (i.e.the flared electrodes), and coupling to spurious modes occurs. As aresult, the optical modulation in the active section 6 will not be inconcert with the inputted electrical signal to the optical modulator.

SUMMARY OF THE INVENTION

[0016] Accordingly, the present invention is directed to an opticalmodulator that substantially obviates one or more of the problems due tolimitations and disadvantages of the related art.

[0017] The present invention provides an optical modulator with enhancedground plane integrity to minimize loss of signal energy and to preventthe introduction of extraneous modes into the modulated optical signal.

[0018] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0019] To achieve these and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described, an opticaldevice of the present invention includes a grounded base; an opticalmodulator chip having a top surface, a back surface and side surfaces,wherein the optical modulator chip is positioned on the grounded basewith the back surface of the optical modulator chip facing the groundedbase; and a first ground electrode, a signal electrode and a secondground electrode located over the top surface of the optical modulatorchip, wherein the first and second ground electrodes are respectivelyconnected to first and second extended resistive electrodes that extenddown at least one side of the optical modulator chip and connect to thegrounded base.

[0020] In another aspect, an optical device of the present inventionincludes: a grounded base; a transition chip for interconnecting anoptical modulator chip having a top surface, a back surface and sidesurfaces, wherein the transition chip is positioned on the grounded basewith the back surface of the transition chip facing the grounded base;and a first ground connection lead, a signal connection lead and asecond ground connection lead located over the top surface of thetransition chip, wherein the first and second ground connection leadsare interconnected to first and second extended resistive connectionleads that extend down at least one side of the transition chip andconnect to the grounded base.

[0021] In another aspect, an optical device of the present inventionincludes: a grounded base; an optical modulator chip positioned on thegrounded base having a top surface, a back surface and side surfaces; afirst ground electrode, a signal electrode and a second ground electrodelocated over the top surface of the optical modulator chip; a transitionchip for interconnecting the optical modulator chip having a topsurface, a back surface and side surfaces, wherein the transition chipis positioned on the grounded base with the back surface of thetransition chip facing the grounded base; and a first ground connectionlead, a signal connection lead and a second ground connection leadlocated on the top surface of the transition chip, wherein the first andsecond ground connection leads are connected to first and secondextended resistive connection leads that extend down at least one sideof the transition chip and connect to the grounded base.

[0022] In another aspect, an optical device of the present inventionincludes: a grounded base; an optical modulator chip having a topsurface, a back surface and side surfaces, wherein the optical modulatorchip is positioned on the grounded base with the back surface of theoptical modulator chip facing the grounded base; at least one groundelectrode and a signal electrode located over the top surface of theoptical modulator chip, wherein the at least one ground electrode isconnected to an extended resistive electrode that extends down one sideof the optical modulator chip and connects to the grounded base; and atransition chip for interconnecting the optical modulator chip having atop surface, a back surface and side surfaces, wherein the transitionchip is positioned on the grounded base with the back surface of thetransition chip facing the grounded base.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate exemplaryembodiments of the invention and together with the description serve toexplain the principles of the invention.

[0024]FIG. 1 shows a top view of a prior art optical modulation device.

[0025]FIG. 2 shows the side view of prior art optical modulator chipelectrodes 31/41/31′ terminating on the top surface of the opticalmodulator chip.

[0026]FIG. 3 shows a side view of an optical modulator chip on agrounded base illustrating a first exemplary embodiment of the presentinvention.

[0027]FIG. 4 shows a bottom view of an optical modulator chip on agrounded base illustrating a second exemplary embodiment of the presentinvention.

[0028]FIG. 5 shows a side view of an optical modulator chip illustratinga third exemplary embodiment of the present invention.

[0029]FIG. 6 illustrates a top view of a prior art device using atransition chip for interconnecting the optical modulator chip toexternal connections.

[0030]FIG. 7 illustrates a side view of prior art transition chipconnection leads 23/24/23′ terminating on the top surface of thetransition chip.

[0031]FIG. 8 shows a side view of a transition chip on a grounded baseillustrating a fifth exemplary embodiment of the present invention.

[0032]FIG. 9 illustrates a bottom view of a transition chip illustratinga sixth exemplary embodiment of the present invention.

[0033]FIG. 10 shows a side view of a transition chip on a grounded baseillustrating a seventh exemplary embodiment of the present invention.

[0034]FIG. 11 illustrates three ways in which the ground connectionleads can extend down sides of a transition chip in accordance with thepresent invention.

[0035]FIG. 12 illustrates a modulator device having only single groundelectrode that can be modified in accordance with the present invention.

[0036]FIG. 13 illustrates a modulator device having planar groundelectrodes that can be modified in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.The present invention is particularly useful in optical modulators andswitches for optical telecommunications network systems that carryoptical communications signals, such as wavelength division multiplexed(WDM) signals, over optical fibers.

[0038]FIG. 3 illustrates a first exemplary embodiment of the invention,as incorporated into an optical modulation device like shown in FIG. 1,viewed in the direction A-A of FIG. 1. As shown in FIG. 3, the groundelectrodes 31/31′ of the optical modulator chip 2 are connected toextended resistive electrodes 32/32′ that extend down the side surfaceof the optical modulator chip 2. FIG. 3 also shows the buffer layer 8terminating at the edge of the top surface of the optical modulator chip2. In the alternative, the buffer layer 8 may be omitted from thedevice. The extended resistive electrodes 32/32′ contact the groundedbase 1 near the back surface of the optical modulator chip 2. Therefore,the extended resistive electrodes 32/32′ are connected by the groundedbase 1 on the back surface of the optical modulator chip 2. In thealternative, the grounded base 1 can be close to the side surface of theoptical modulator chip 2 shown in FIG. 3 as a result of the opticalmodulating chip residing in a well of the grounded base 1 with thelengths of sides of the extended resistive electrodes 32/32′ along thesides of the optical modulator chip 2 directly in contact to the innersidewall of the well in the grounded base.

[0039]FIG. 4 illustrates a second exemplary embodiment of the invention,as incorporated into an optical modulation device like shown in FIG. 1,with a bottom view of the back surface of an optical modulator chip 2which is the surface opposite to the surface having electrodes31/41/31′. As shown in FIG. 4, the ground electrodes 31/31′ areconnected to extended resistive electrodes 32/32′ that extend from thetop surface of the optical modulator chip 2, across the side surface ofthe optical modulator chip 2 and onto the back surface of the opticalmodulator chip 2. The extended resistive electrodes 32/32′ areinterconnected together at a portion 10 on the back surface of theoptical modulator chip and directly connected to the grounded base 1which lies directly underneath the optical modulator chip 2. FIG. 4 alsoshows that the buffer layer 8 extends down the side surface of theoptical modulator chip 2. In the alternative, the buffer layer 8 may beomitted from the side surface of the optical modulator chip 2 dependingon the cut (i.e., z or x cut) of the optical modulator chip.

[0040]FIG. 5 illustrates a third exemplary embodiment of the invention,as incorporated into an optical modulation device like shown in FIG. 1,viewed in the direction A-A of FIG. 1. As shown in FIG. 3, the groundelectrodes 31/31′ of the optical modulator chip 2 connect to extendedresistive electrodes 32/32′ that extend down the side surface of theoptical modulator chip 2 and contact the grounded base 1. In addition,as shown in FIG. 5, the extended resistive electrodes 32/32′ areinterconnected together at a portion 11 on the side surface of theoptical modulator chip 2. In the alternative, the grounded base 1 can beclose to the side surface of the chip shown in FIG. 5 as a result of theoptical modulating chip residing in a well of the grounded base 1 withthe lengths of sides of the extended resistive electrodes 32/32′ alongthe sides of the optical modulator chip directly in contact to the innersidewall of the well in the grounded base.

[0041] The extended resistive electrodes 32/32′ in FIGS. 3, 4 and 5and/or the interconnect 10/11 shown in FIGS. 4 and 5, can be comprisedof several resistive coatings applied separately or just a singularlyapplied resistive coating. The resistive coating or coatings comprisingthe extended resistive electrodes 32/32′ and/or interconnections 10/11can be carbon-based, ceramic-based or thin film based resistors or otherresistive means. For example, the coatings can be a carbon paint,Alumina or Silicon (either doped or undoped). In addition, the extendedresistive electrodes and the interconnections can be comprised of thesame resistive coating or different resistive coatings. By connectingthe ground electrode or electrodes of a modulator to an extendedresistive electrode or extended resistive electrodes that extend downthe side surface of the optical modulator chip so as to connect to thegrounded base and/or interconnect on a side of the optical modulatorchip, the opportunity for extraneous mode coupling into parallel platemodes or other spurious modes is decreased.

[0042] In the alternative to the use of extended resistive electrodes onthe optical modulator chip 2, the same advantages can be realized with atransition chip 7 having extended resistive connection leads, if atransition chip is used for interconnection to the optical modulatorchip. However, a transition chip with extended resistive connectionleads can also be used with a optical modulator chip having extendedresistive electrodes. Furthermore, a conventional transition chip can beused with an optical modulator chip having extended resistive electrodesas described above.

[0043]FIG. 6 discloses the prior art structure for connecting an opticalmodulating chip 2 with a transition chip 7. The transition chip 7 has afirst ground connection lead 23, a signal connection lead 24 and asecond ground connection lead 23′ on the top surface of the transitionchip 7. The ground connection leads 23/23′ of the transition chip 7 arerespectively connected to the flared ground electrodes 31/31′ with wires311/311′ and the signal connection lead 24 of the transition chip 7 isconnected to the flared signal electrode 41 with a wire 411.

[0044]FIG. 7 shows a side view of the transition chip 7 in the directionshown as B-B in FIG. 7. The prior art transition chip leads 23/24/23′,as shown in FIG. 7, terminate at the edge of the transition chip 7. Thebody of the transition chip 7 is usually comprised of an insulatingmaterial. In addition or in the alternative to the first, second andthird embodiments disclosed above in FIGS. 3, 4 and 5, the ground planeintegrity can be enhanced by extending resistive connection leads downthe side surfaces of the transition chips used for interconnection to anoptical modulator.

[0045]FIG. 8 illustrates a fifth exemplary embodiment of the invention,as incorporated into an optical modulation device like shown in FIG. 6,viewed in the direction B-B of FIG. 6. As shown in FIG. 8, the groundconnection leads 23/23′ of the transition chip 2 are connected toextended resistive connection leads 33/33′ that extend down the sidesurface of the transition chip 7. The extended resistive connectionleads 33/33′ contact the grounded base 1 near the back surface of thetransition chip 7. Therefore, the extended resistive connection leads33/33′ are connected by the grounded base 1 on the back surface of thetransition chip 7. In the alternative, the grounded base 1 can be closeto the side surface of the transition chip 7 shown in FIG. 8 as a resultof the transition chip residing in a well of the grounded base 1 withthe lengths of sides of the extended resistive connection leads alongthe sides of the transition chip directly in contact to the innersidewall of the well in the grounded base.

[0046]FIG. 9 illustrates a sixth exemplary embodiment of the invention,as incorporated into an optical modulation device like shown in FIG. 6,with a bottom view of the back surface of a transition chip 7 which isthe surface opposite to the surface having leads 23/24/23′. As shown inFIG. 9, the ground connection leads 23/23′ on the top surface of thetransition chip are connected to extended resistive connection leads33/33′ that extend across the side surface of the transition chip andonto the back surface of the transition chip 7. The extended resistiveconnection leads 33/33′ are interconnected together at a portion 10 a onthe back surface of the transition chip 7 and connected to the groundedbase 1 which lies beneath the transition chip 7.

[0047]FIG. 10 illustrates a seventh exemplary embodiment of theinvention, as incorporated into an optical modulation device like shownin FIG. 6, viewed in the direction B-B of FIG. 6. As shown in FIG. 10,the ground connection leads 23/23′ on the top surface of the transitionchip 7 are connected to extended resistive connection leads 33/33′ thatextend across the side surface of the transition chip and areinterconnected together at a portion 11 a. The extended resistiveconnection leads 33/33′ extend down the side surface of the transitionchip to the bottom edge of the side surface in order to contact thegrounded base 1. In the alternative, the grounded base 1 can be close tothe side surface of the transition chip shown in FIG. 10 as a result ofthe transition chip residing in a well of the grounded base 1 with thelengths of sides of the extended resistive connection leads along thesides of the transition chip directly in contact to the inner sidewallsof the wells in the grounded base.

[0048] The extended resistive connection leads 33/33′ in FIGS. 8, 9 and10 and/or the interconnections 10 a/11 a shown in FIGS. 9 and 10, can becomprised of several resistive coatings applied separately or just asingularly applied resistive coating. The resistive coating or coatingscomprising the extended resistive connection leads 33/33′ and/orinterconnections 10 a/11 a can be carbon-based, ceramic-based or thinfilm based resistors or other resistive means. For example, the coatingscan be a carbon paint, Alumina or Silicon (either doped or undoped). Inaddition, the extended resistive connection leads 33/33′ and theinterconnections can be comprised of the same resistive coating ordifferent resistive coatings. By connecting a ground connection lead toan extended resistive connection lead electrodes that extend down theside surface of the optical modulator chip so as to connect to thegrounded base and/or interconnect to another extended resistiveconnection lead on a side of the optical modulator chip, the opportunityfor extraneous mode coupling into parallel plate modes or other spuriousmodes is decreased.

[0049]FIG. 11 illustrates other examples of how the ground connectionleads 23/23′ of the transition chip 7 can be interconnected by extendedresistive connection leads 33/33′ extending along side surface AA thatwould be next to the optical modulator chip 2, opposing side surfaces BBfor interconnection on the back surface of the transition chip 7 or sidesurface CC near where the signal is initially inputted. FIG. 11 alsoillustrates how in the alternative or in addition to the extendedresistive connection leads, resistive vias 43 can be formed in thetransition chip 7 so as to connect the ground connection leads 23/23′ tothe grounded base underneath the transition chip 7 by resistive meansgoing through the transition chip 7. There can be one or more resistivevias in the transition chip for each of the connection leads 23/23′.Although the transition chip 7 is shown as trapezoidal-shaped, thetransition chip can be any polygonal shape that facilitates externalinterconnection to the optical modulator chip 2. Furthermore, instead oftwo transition chips being used to interconnect the optical modulatorchip 2, a single transition chip that extends along the length of theoptical modulator chip can be used for external interconnection to theoptical modulator chip 2. When using a single transition chip, theextended ground connection leads will be on either or both of the sideslike AA and CC in FIG. 11.

[0050] In addition, it is within the scope of the present invention,that side surfaces of both the optical modulator chip and the transitionchip can have resistive extensions that are interconnected on the sidesurfaces of each respective chip and to one another. Also, both theoptical modulator chip and the transition chip can have resistiveextensions on side surfaces of the chips and on the back surfaces of thechips, wherein resistive extensions of each chip on the sides of eachchip are interconnected.

[0051] Furthermore, the present invention can be used in other types ofmodulator devices. For example, as shown in FIG. 12, a modulator device200 having a single ground electrode 3 can have extended resistiveelectrodes extending down the side D that contact the grounded baseunderneath and may also be interconnected like the second and thirdembodiments. The device in FIG. 12 is a Mach-Zehnder interferometer withwaveguide 34 and a signal electrode 4 with flared ends 41 in addition tothe ground electrode 3 with flared ends 31. However, the presentinvention can be used in other single ground electrode modulators (e.g.phase shifters).

[0052]FIG. 13 illustrates how the present invention can be used in amodulator device 300 having planar ground electrodes. The modulatordevice in FIG. 13 has a first planar ground electrode 3, a second planarground electrode 3′, a waveguide 34 and signal electrode 4 with flaredends 41. The planar ground electrodes 3/3′ are connected to extendedresistive electrodes extending down the sides as shown by E, downadjoining sides as shown by F1/F2, or down all four sides to contact thegrounded base underneath. In addition, the extended resistive electrodesmay also be interconnected like the second and third embodiments. It isalso within the scope of the present invention that the exemplaryembodiments can be used to modify optical modulators having more thantwo ground electrodes.

[0053] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the optical modulator of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

What is claimed is:
 1. An optical device comprising: a grounded base; anoptical modulator chip having a top surface, a back surface and sidesurfaces, wherein the optical modulator chip is positioned on thegrounded base with the back surface of the optical modulator chip facingthe grounded base; and a first ground electrode, a signal electrode anda second ground electrode located over the top surface of the opticalmodulator chip, wherein the first and second ground electrodes areconnected to first and second extended resistive electrodes that extenddown at least one side of the optical modulator chip and are connectedto the grounded base.
 2. The optical device of claim 1, wherein thefirst and second extended resistive electrodes are connected to eachother on the back surface of the optical modulator chip.
 3. The opticaldevice of claim 2, wherein the extended resistive electrodes and theconnection of the extended resistive electrodes are comprised of asingle layer of resistive material.
 4. The optical device of claim 1,wherein lengths of the extended resistive electrodes on a side of theoptical modulator chip abut against the grounded base as a result of theoptical modulator chip residing in a well within the grounded base. 5.The optical device of claim 2, wherein the extended resistive electrodesand the connection of the extended resistive electrodes are comprised ofcarbon-based, ceramic-based or thin film based resistive materials. 6.The optical device of claim 1, wherein the first and second extendedresistive electrodes are connected to each other on a side surface ofthe optical modulator chip.
 7. The optical device of claim 6, whereinthe extended resistive electrodes and the connection of the extendedground electrodes are comprised of a single layer of resistive material.8. The optical device of claim 6, wherein the extended resistiveelectrodes and the connection of the extended ground electrodes arecomprised of different layers of resistive material.
 9. The opticaldevice of claim 1, wherein an insulating buffer layer is on the top andside surfaces between the electrodes and the optical modulator chip. 10.An optical device comprising: a grounded base; a transition chip forinterconnecting an optical modulator chip having a top surface, a backsurface and side surfaces, wherein the transition chip is positioned onthe grounded base with the back surface of the transition chip facingthe grounded base; and a first ground connection lead, a signalconnection lead and a second ground connection lead located over the topsurface of the transition chip, wherein the first and second groundconnection leads are interconnected to first and second extendedresistive connection leads that extend down at least one side of thetransition chip and are connected to the grounded base.
 11. The opticaldevice of claim 10, wherein the first and second extended groundconnection leads are comprised of a single layer of resistive material.12. The optical device of claim 11, wherein the extended resistiveconnection leads and the interconnection of the extended resistiveconnection leads are comprised of carbon-based, ceramic-based or thinfilm-based resistive materials.
 13. The optical device of claim 10,wherein lengths of the extended resistive connection leads on a side ofthe transition chip abut against the grounded base as a result of thetransition chip residing in a well within the grounded base.
 14. Theoptical device of claim 10, wherein the extended resistive connectionleads and the interconnection of the extended ground connection leadsare comprised of different layers of resistive material.
 15. The opticaldevice of claim 10, wherein only one transition chip runs along a sideof the optical modulator and is used for external interconnection to theoptical modulator chip.
 16. The optical device of claim 10, wherein thefirst and second extended resistive connection leads extend downopposing side surfaces of the transition chip.
 17. The optical device ofclaim 10, wherein resistive vias interconnect the ground connectionleads to the grounded base through the transition chip.
 18. An opticaldevice comprising: a grounded base; an optical modulator chip positionedon the grounded base having a top surface, a back surface and sidesurfaces; a first ground electrode, a signal electrode and a secondground electrode located over the top surface of the optical modulatorchip; a transition chip for interconnecting the optical modulator chipto external connections having a top surface, a back surface and sidesurfaces, wherein the transition chip is positioned on the grounded basewith the back surface of the transition chip facing the grounded base;and a first ground connection lead, a signal connection lead and asecond ground connection lead located on the top surface of thetransition chip, wherein the first and second ground connection leadsare connected to first and second extended resistive connection leadsthat extend down at least one side of the transition chip and areconnected to the grounded base.
 19. The optical device of claim 18,wherein the first and second ground electrodes are connected to firstand second extended resistive electrodes that extend down at least oneside of the optical modulator chip and are connected to the groundedbase.
 20. The optical device of claim 19, wherein the first and secondextended resistive electrodes are connected to each other on the backsurface of the optical modulator chip.
 21. The optical device of claim18, wherein the first and second extended resistive connection leads areconnected to each other on the back surface of the transition chip. 22.The optical device of claim 20, wherein the extended resistiveelectrodes and the connection of the extended resistive electrodes arecomprised of a single layer of resistive material.
 23. The opticaldevice of claim 21, wherein the extended resistive connection leads andconnection of the extended resistive connection leads are comprised of asingle layer of resistive material.
 24. An optical device comprising: agrounded base; an optical modulator chip having a top surface, a backsurface and side surfaces, wherein the optical modulator chip ispositioned on the grounded base with the back surface of the opticalmodulator chip facing the grounded base; at least one ground electrodeand a signal electrode located over the top surface of the opticalmodulator chip, wherein the at least one ground electrode is connectedto an extended resistive electrode that extends down one side of theoptical modulator chip and is connected to the grounded base; atransition chip for interconnecting the optical modulator chip having atop surface, a back surface and side surfaces, wherein the transitionchip is positioned on the grounded base with the back surface of thetransition chip facing the grounded base; and at least one connectionlead located on the top surface of the transition chip.
 25. The opticaldevice of claim 24, wherein the at least one ground electrode is aplanar electrode.
 26. The optical device of claim 24, wherein the atleast one ground electrode is comprised of two or more ground electrodeseach being connected to extended resistive electrodes that are connectedto the grounded base.
 27. The optical device of claim 26, wherein theextended resistive electrodes are connected to each other on a side ofthe optical modulator chip.
 28. The optical device of claim 26, whereinthe extended resistive electrodes are connected to each other on theback surface of the optical modulator chip.
 29. The optical device ofclaim 26, wherein the extended ground electrodes extend down differentsides of the optical modulator chip.
 30. The optical device of claim 24,wherein more than one extended resistive electrode is connected to aground electrode.
 31. The optical device of claim 30, wherein theextended resistive electrodes extend down different sides of the opticalmodulator chip.
 32. An optical device comprising: a grounded base; anoptical modulator chip having a top surface, a back surface and sidesurfaces, wherein the optical modulator chip is positioned on thegrounded base with the back surface of the optical modulator chip facingthe grounded base; at least one ground electrode and a signal electrodelocated over the top surface of the optical modulator chip; a transitionchip for interconnecting the optical modulator chip having a topsurface, a back surface and side surfaces, wherein the transition chipis positioned on the grounded base with the back surface of thetransition chip facing the grounded base; and at least one connectionlead located on the top surface of the transition chip, wherein aresistive via through the transition chip interconnects the at least oneground connection lead with the grounded base.
 33. The optical deviceaccording to claim 32, wherein there are one or more conductive vias foreach connection lead.
 34. An optical device comprising: a grounded baseon which an optical modulator chip is positioned; a first groundelectrode, a signal electrode and a second ground electrode located onthe optical modulator chip; and wherein the first and second groundelectrodes are connected to each other and the grounded base withresistive electrodes on a side of the optical modulator chip.
 35. Anoptical device comprising: a grounded base on which an optical modulatorchip is positioned; a first ground electrode, a signal electrode and asecond ground electrode located on the optical modulator chip; atransition chip having a first connection lead connected to the firstground electrode, a signal connection lead connected to the signalelectrode and a second connection lead connected to the second groundelectrode; and wherein the first and second connection leads areconnected to each other and the grounded base with resistive connectionleads on a side of the transition chip.